The present invention relates to a reclining angle adjustment device for adjusting the angle of inclination of the seat back of a reclining seat in a motor vehicle, i.e., the reclining angle of the reclining seat.
There are known reclining angle adjustment devices in which the reclining angle is adjusted by means of a planetary gear mechanism.
The planetary gear mechanism employed in the reclining angle adjustment device is composed of a first arm having an external gear, a second arm having an internal gear with more teeth than the external gear, and a shaft having a concentric portion inserted through the center of the external gear and an eccentric portion inserted through the center of the internal gear. The external and internal gears are held in mesh with each other through the shaft. When the shaft is rotated about its own axis, the angle of the first arm with respect to the second arm is varied. Therefore, by attaching one of the first and second arms to the frame of the seat back of a seat and the other arm to the frame of the seat cushion thereof, the reclining angle of the seat can be adjusted by rotating the shaft.
The first arm, the second arm, and the shaft are machined so that they mesh without biting into each other irrespective of machining tolerances. Therefore, there are always gaps or backlashes between fitting and meshing members of the first arm, the second arm, and the shaft. These gaps or backlashes result in unwanted motion of the seat back with respect to the seat cushion, making the person on the seat uncomfortable and producing noise. While the motor vehicle is running, the first arm may vibrate with respect to the second arm due to vibration of the motor vehicle, and the shaft may temporarily become free to rotate of its own accord about its own axis, so that the second arm and hence the seat back may be tilted even when no angle adjustment is made for the seat back. The discomfort which the person on the seat may suffer, the noise produced by the seat back, and the accidental rotation of the shaft tend to increase with increased gaps due to localized machining tolerances of the members.